This invention relates to an actuator system, and more particularly to such a system which is ambient temperature conpensated and useful, for example, as an electrical relay which may be actuated at low power levels.
Specifically, known relay actuator systems in the field of this invention have used a length of a special alloy actuating wire (e.g., a nickel-titanium alloy such as Nitinol) which when stretched from its original length to a second length by a spring or the like and heated above an actuation temperature undergoes a change in its modulus of elasticity from a relatively low value (e.g. 3.times.10.sup.6 psi or 2.07.times.10.sup.10 N/m.sup.2) to a relatively high value (e.g., 12.times.10.sup.6 psi or 8.27.times.10.sup.10 N/m.sup.2). This change in modulus of elasticity causes the length of the wire to shrink from its second length to its original length thus causing an increase in tension in the wire which acts to move an actuator arm or the like. Upon cooling, the wire is again stretched back to its second length by the spring. Reference may be made to U.S. Pat. Nos. 3,634,803 and 3,652,969 which illustrate known relay actuator systems in the same general field as the present invention.
While these prior art relay actuator systems offer many advantages, changes in ambient temperature cause problems. For example, upon ambient temperature increasing from room temperature to a higher ambient temperature, this higher ambient temperature being below the above-mentioned actuation temperature, the length of the wire would gradually shrink or contract thus causing the contacts of the relay to creep closed (or open). Also, upon energizing the wire at high ambient temperatures with a constant current at the power level required to insure actuation of the relay at normal or low ambient temperatures, the wire could be heated appreciably above the above-mentioned actuation temperature. It has been found that overheating the wire above the actuation temperature may significantly reduce the operating life of the relay actuator system and may cause system failure.